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idavis
05-18-2007, 02:50 AM
I want to thank Ton for spawning such an interesting discussion. I
have missed these discourses on biomch-l that were so pervasive in the
days of Herman Woltring. Our lab group just discussed this topic today
in one of our meetings and agree, in theory, with both Andy's and Ton's
elegantly presented viewpoints. We are going to see another 'growth
spurt' in prosthetic technology, as we have during previous wars.
Even if science were to prove that there was not an advantage today, it
is very possible, and likely, that technology will advance faster than
human performance, necessitating separate divisions.


On May 18, 2007, at 12:30 PM, van den Bogert, Ton wrote:

> I am surprised by the attempts to argue that this prosthetic technology
> provides no advantage. Why not allow the idea that this technology
> works better (for specific movement tasks, e.g. 100 m sprint) than the
> natural limb? Would that not be much more inspiring to those with
> disabilities (and to scientists)? The remarkable performance of Mr.
> Pistorius shows that this idea must be seriously considered.
>
> First of all, energy cost is probably not a major consideration for a
> 100 m sprint. Studies showing higher oxygen uptake in amputee gait may
> not be relevant to this issue. In sprinting, the main goal is to
> maximize total net power output of all muscles, in order to increase
> kinetic energy (in the first phase of the race) and to do work against
> air drag (in the last part of the race).
>
> If my scientific intuition is right, it is only a matter of time before
> an amputee will break a world record in track and field. At that
> point,
> there will have to be separate competitions and records for able-bodied
> athletes, as Andy Ruina suggested. This is not really different from
> wheelchair athletes in marathons. They are much faster than the
> runners, but are considered to be in a different category. Question is
> (for the sports organizations) whether to wait until a gold medal or a
> world record forces the issue.
>
> If science is to help determine whether or not a prosthetic foot is
> advantageous, here is my theory, a hypothesis and a proposal for how to
> test it.
>
> Theory
>
> I have not looked at the biomechanics literature on sprinting, but I
> suspect that it is known that ankle plantarflexion has a substantial
> contribution to mechanical power output. The prosthetic "ankle" has no
> net positive power output, so this would seem to be a great
> disadvantage
> to the amputee athlete. However, we can't look at joints in isolation.
> The prosthetic foot may allow the hip and knee extensors to function
> differently.
>
> It is theoretically possible that a compliant foot allows hip and knee
> extensors to produce more net power over the gait cycle. This is quite
> similar to the principle of a muscle acting in series with a compliant
> tendon. See, for example, Glen Lichtwark's recent paper in J Biomech
> [1]. The basic idea is that muscle fibers can shorten while the tendon
> lengthens and stores energy. When considering a limb, we have multiple
> joints in series. In the amputee, therefore, knee and hip extension
> may
> start earlier in the stance phase than in the able-bodied athlete,
> storing the extra energy in the compliant foot. That energy will be
> released at the end of the stance phase.
>
> Hypotheses
>
> (1) Joint power at knee and hip are greater in an amputee sprinter than
> in an able-bodied sprinter.
> (2) This increase in knee and hip power is greater than the power
> produced at the ankle in an able-bodied athlete.
>
> Methods
>
> The analysis can be done with standard inverse dynamics methods. It
> will be necessary to get data for the entire 100 m race. It will he
> difficult to get force plate data for every stride. However, sprinting
> has no double support phase, so this can be done quite well with a
> whole
> body model which does not require force plate data.
>
> It is probably best to compare this highly trained amputee to a group
> of
> able-bodied sprinters who have similar 100 m times. If they run the
> same speed, hypothesis (2) should probably be worded as "equal to"
> instead of "greater than". This is because the same speed implies that
> total mechanical power output is the same.
>
> Why is this important?
>
> If this theory turns out to be correct, we have a scientific basis for
> optimizing the performance of these devices and for developing novel
> movement strategies to use them. We will make great strides (:-) in
> improving locomotor function for all amputees, not just elite athletes.
> If we keep insisting that "of course" these devices are not as good as
> real feet, we have little incentive for research and we are telling
> them
> that, "of course" they will always be handicapped.
>
> References
>
> [1] Lichtwark GA, Wilson AM (2007) Is Achilles tendon compliance
> optimised for maximum muscle efficiency during locomotion? J Biomech
> 40: 1768-1775.
>
> --
>
> Ton van den Bogert
> Department of Biomedical Engineering
> Cleveland Clinic Foundation
> http://www.lerner.ccf.org/bme/bogert/
> (apologies for the advertising below, I have no control over this)
>
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Irene Davis, PhD, PT, FACSM
Director of Research, Drayer Physical Therapy Institute
Professor, Dept. of Physical Therapy
305 McKinly Lab
University of Delaware
Newark, DE 19716

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